1. Field of the Invention
The present invention relates generally to a broadcast signal retransmission system and method and, more particularly, to using illuminating visible-light communication system, wherein individual broadcast signals of available channels from a received multi-channel broadcast signal are transmitted using illuminating visible-light communication over power lines.
2. Description of the Related Art
In recent years, radio communication systems have come into widespread use with the popularization of portable terminals. Owing to a shortage of available frequency resources, infrared communication systems using infrared rays, which have wavelengths shorter than those of radio waves, have been actively developed. However, in addition to the shortage of frequency resources, it has been confirmed that radio waves have detrimental influence on various medical or precision instruments. Infrared rays may also be detrimental to the human body in particular circumstances. In safety aspects of communication, visible-light communication systems attract much attention.
Development of blue light-emitting diodes (LEDs) has enabled realization of white LEDs. Compared with an incandescent lamp or fluorescent lamp, a white LED consumes much less power, is smaller, and has a longer lifetime. Research efforts are ongoing to transmit signals using white LEDs by controlling on/off operations or the light amount of the white LEDs.
Active research is taking place to integrate a signal transmission function of white LEDs with a power line communication (PLC) system. Such an integrated communication system utilizing visible light is not detrimental to the human body, enables safe communication, and is expected to provide worthwhile applications.
FIG. 1 is a block diagram showing a conventional broadcast signal retransmission system.
As shown in FIG. 1, the broadcast signal retransmission system comprises an information source 10, a power line modem 12, outlets 14 and 16 interconnected by a power line, an LED lighting fixture 20, and a light-receiving terminal 30.
The information source 10 is an information output apparatus providing various kinds of information, and may be a computer or a device composed of a tuner and receiver for television, cable television and radio broadcasting. Hence, broadcast information may be a video, audio, voice, still image, character data and others.
The power line modem 12 modulates information from the information source 10 and superimposes the modulated information on a power wave carried on the power line interconnecting the outlets 14 and 16 to transmit the modulated information through the power line. Although an ordinary PLC system includes a demodulating means to support two-way communication, the broadcast signal retransmission system is one-way and does not include a demodulating means. Frequency division multiplexing may be used for multiplexing information. The power line may be an indoor or outdoor electric power transmission line.
The LED lighting fixture 20 is connected to the power line, and illuminates the vicinity thereof. The LED lighting fixture 20 may be installed at the indoor ceiling of a house and may be used for various types of illumination including spot illumination.
The LED lighting fixture 20 includes an AC/DC converter 22, a band pass filter (BPF) 24, a coupler 26, and a plurality of LEDs 28. Because DC power is needed to drive the LEDs 28 to emit light, the AC/DC converter 22 converts AC power from the power line into DC power. The AC/DC converter 22 adjusts the voltage level of the DC power according to an operating voltage of the LEDs 28, and supplies operating power to the BPF 24.
The BPF 24 acts to extract an information signal superimposed on the power line, and may selectively extract a single information signal from multiple information signals.
The coupler 26 couples the information signal extracted by the BPF 24 to the wave of the DC power converted by the AC/DC converter 22. Hence, the level of the voltage fed to the LEDs 28 can be changed according to the information signal, thereby making it possible to control the amount of light of the LEDs 28 and an on/off operation thereof. For example, the power from the AC/DC converter 22 can be controlled by the information signal from the BPF 24 to turn on and off the LEDs 28.
The LEDs 28 are primarily light sources for illumination, and may be white LEDs or a combination of red, green and blue LEDs. The LEDs 28 are driven by the power from the coupler 26 to emit light. Because LED(s) 28 has a fast response time, the amount of light of LED(s) 28 or the on/off operation thereof can be controlled by an information signal, enabling transmission of the information signal in the form of light produced by the LED 28 or LEDs (e.g., combination of red, green and blue).
The light-receiving terminal 30 includes a light-receiving means to receive light emitted from the LED lighting fixture 20, and extracts an information signal from the received light and demodulates the extracted information signal to produce desired information. The light-receiving terminal 30 may be any appliance having a light-receiving means, such as a personal computer, portable terminal, mobile phone, audio instrument or television set.
However, in the conventional broadcast retransmission system, the broadcast signal transmitted through the power line from the information source 10 is a single channel signal; therefore identical information is distributed along available power lines. Consequently, users have no choice but to receive the same information retransmitted by the retransmission system through the light-receiving terminals 30. That is, a user cannot selectively receive a retransmitted broadcast signal of a desired channel according to the user's taste.